On second thought, fuel flow as volume is OK because fuel mass and temp roughly equal pressure.
If it's OK to use gasoline information, here are some more sources. Diesel isn't quite the same because the Bosch VW pumps operate like a pressure wave. In terms of fuel flow per injector, my best guess is that the newer common rails operate more like gasoline engine fuel injectors because they are releasing fuel out of a common pressurized rail. The difference is that the new TDI common rail is 20,000-28,000psi vs. a traditional gasoline fuel injection system of about 60-80 psi.
http://www.rceng.com/technical.aspx
I don't know what the duty cycle of the newest TDI injector is and I don't think that is even applicable because the duty cycle is a % time the solenoid opens the injector. The older TDIs just opened in response to a pressure wave, the newer TDI used a solenoid, the newest use a piezoelectric crystal to inject fuel. But hopefully this will get you started!